Four security guards are in police custody in Port Moresby, as investigations continue into one of the city's biggest bank robbery in history.

A record six-million Kina, was robbed from the May Bank last Friday, when security guards escorting the money to the Bank of Papua New Guinea, turned on their escort commander, taking the cash trunks in broad daylight, at Down Town Port Moresby.

National Capital District Chief of Police Operations Chief Inspector, Perou N'dranou told NBC News, an investigation team is already in place and is making headway in their probe.